This invention relates to a casing of a watch like a wrist watch.
Generally, a casing of a watch like a wrist watch, as shown in appended FIGS. 1 and 2, is exposed to the atmosphere for a long time and, in addition, kept in contact with the skin of a human being. Accordingly, the casing tends to be corroded by the sweat or rainwater deposited thereon. Further, the surface of the casing is likely to be damaged by external impacts. It follows that the material of a watch case should have a corrosion resistance and a hardness high enough to withstand the severe wear conditions in which the watch case is placed.
Austenite stainless steel (for example, AISI 304) is widely used as the material of a watch case. Indeed, this material is high in corrosion resistance, but is not satisfactory in terms of hardness. Specifically, Vickers hardness (H.sub.v) of this material is about 250. Thus, where a watch case is made of stainless steel, much labor is required for the final step of planishing. Moreover, about six months to about one year after the use, the surface of the watch case tends to bear bruises, resulting in the loss of metal luster and beauty.
To remove the drawbacks mentioned above, various materials are under development for use as the material of a watch case. For example, available is a watch case of a high hardness prepared by subjecting a sintered alloy of Cr-Mo-Wo-Fe system, which is inferior in cutting of machining And, the article obtained by a powder metallurgical method is not satisfactory in dimensional accuracy and, thus, not suitable for use as a watch case requiring a high degree of precision. In addition, the article mentioned is weak against impacts and bears a great number of micro pores, rendering it difficult to supply surface treatments such as planishing to the article.